Scroll machines include an orbiting scroll member intermeshed with a non-orbiting scroll member to define a series of compression chambers. Rotation of the orbiting scroll member relative to the non-orbiting scroll member causes the compression chambers to progressively decrease in size and cause a fluid disposed within each chamber to be compressed.
During operation, the orbiting scroll member orbits relative to the non-orbiting scroll member through rotation of a drive shaft, which is typically driven by an electric motor. Because the drive shaft is driven by an electric motor, energy is consumed through rotation of the orbiting scroll member. Energy consumption increases with increasing discharge pressure as the scroll machine is required to perform more work to achieve higher pressures. Therefore, if the incoming vapor (i.e., vapor introduced at a suction side of the scroll machine) is at an elevated pressure, less energy is required to fully compress the vapor to the desired discharge pressure.
Vapor injection systems may be used with scroll machines to improve efficiency by supplying intermediate-pressure vapor to the scroll machine. Because intermediate-pressure vapor is at a somewhat higher pressure than suction pressure and at a somewhat lower pressure than discharge pressure, the work required by the scroll machine in producing vapor at discharge pressure is reduced.
Vapor injection systems typically extract vapor at an intermediate pressure from an external device commonly referred to as an economizer such as a flash tank or a heat plate exchanger for injection into a compression chamber of a scroll machine. The flash tank or plate heat exchanger is typically coupled to the scroll machine and a pair of heat exchangers for use in improving system capacity and efficiency. The pair of heat exchangers each serve as a condenser and an evaporator of the system depending on the mode (i.e., cooling or heating).
In operation, the flash tank receives liquid refrigerant from the condenser for conversion into intermediate-pressure vapor and sub-cooled liquid refrigerant. Because the flash tank is held at a lower pressure relative to the inlet liquid refrigerant, some of the liquid refrigerant vaporizes, elevating the pressure of the vaporized refrigerant within the tank. The remaining liquid refrigerant in the flash tank loses heat and becomes sub-cooled for use by the evaporator. Therefore, conventional flash tanks contain both vaporized refrigerant and sub-cooled liquid refrigerant.
The vaporized refrigerant from the flash tank is distributed to an intermediate pressure input port of the scroll machine, whereby the vaporized refrigerant is at a substantially higher pressure than vaporized refrigerant leaving the evaporator, but at a lower pressure than an exit stream of refrigerant leaving the scroll machine. The pressurized refrigerant from the flash tank allows the scroll machine to compress this pressurized refrigerant to its normal output pressure while passing it through only a portion of the scroll machine.
The sub-cooled liquid is discharged from the flash tank and is sent to one of the heat exchangers depending on the desired mode (i.e., heating or cooling). Because the liquid is in a sub-cooled state, more heat can be absorbed from the surroundings by the heat exchanger, improving the overall heating or cooling performance of the system.
The flow of pressurized refrigerant from the flash tank to the scroll machine is regulated to ensure that only vaporized refrigerant or a minimum amount of liquid is received by the scroll machine. Similarly, flow of sub-cooled liquid refrigerant from the flash tank to the heat exchanger is regulated to inhibit flow of vaporized refrigerant from the flash tank to the evaporator. Conventional flash tanks regulate the flow of liquid refrigerant into the flash tank at an inlet of the tank to control the amount of vaporized refrigerant supplied to the scroll machine and sub-cooled liquid refrigerant supplied to the evaporator during one or both of a cooling mode and a heating mode.